Project 3 will use mouse models of multistage pancreatic carcinogenesis previously developed and concurrently analyzed by Project 1 to investigate the neoplastic microenvironment and its constituent cell types as functions of losses in the INK4a/Arf, p53, and/or SMAD4 tumor suppressors, and of activity of the PI3 Kinase pathway, all in the context of mutationally activated KRAS signaling. Microenvironmental parameters to be assessed include: angiogenesis and the character of the blood vasculature; the association of pericytes with the tumor vasculature; lymphangiogenesis and the morphology of the lymphatic vasculature; the abundance and types of infiltrating (tumor-enhancing) leucocytes and expression/activity of the matrix-degrading enzymes they produce; and the characteristics of the fibroblastic stromal cells. A central goal is to test the hypothesis that the angiogenic phenotype and other features of the neoplastic microenvironment of PanIN and PDAC are differentially regulated by the loss of particular tumor suppressor genes that are signatures of this disease. An ancillary goal, to be pursued in collaboration with Project 2, is to determine the importance of KRAS signaling via the PIS kinase network in the cancer cells for induction of the aberrant tumor microenvironment. Analysis of human tumor biopsies with the Experimental Pathology Core will assess the correlation of genetic and phenotypic parameters identified in the mouse. Neoplastic stage-specific preclinical trial designs will be established and used to test innovative chemotherapeutic regimens, targeted antiangiogenic therapies, and combinations that might guide future human clinical trials. Joint studies with the Imaging Core will develop probes that non-invasively visualize parameters of the microenvironment, both to monitor lesional progression, and responses to therapy. Biomarkers of the cell-of-origin/pancreatic cancer stem cell identified by Project 4 will be used to assess specific responses to therapy and roles in relapse/progression. . These studies, in engineered mouse models of de novo pancreatic cancer, will characterize in unprecedented detail the aberrant lesional microenvironment and its regulation by genetic mutations during multistage progression, and begin knowledge-based pre-clinical therapeutic trials with the potential to reveal strategies that could be translated into improved treatments for the human disease.